Subject: [PATCH 12/13] powerpc/64s: idle POWER9 can execute stop in virtual mode

From: Nicholas Piggin <[email-masked]>
Date: Sun, 6 Aug 2017 03:02:40 +1000

The hardware can execute stop in any context, and KVM does not
require real mode. This saves a switch to real-mode when going
idle.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/idle_book3s.S | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 75746111e2c4..8ac366a51bb5 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -141,7 +141,16 @@ pnv_powersave_common:
 	std	r5,_CCR(r1)
 	std	r1,PACAR1(r13)
 
+BEGIN_FTR_SECTION
+	/*
+	 * POWER9 does not require real mode to stop, and does not set
+	 * hwthread_state for KVM (threads don't share MMU context), so
+	 * we can remain in virtual mode for this.
+	 */
+	bctr
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 	/*
+	 * POWER8
 	 * Go to real mode to do the nap, as required by the architecture.
 	 * Also, we need to be in real mode before setting hwthread_state,
 	 * because as soon as we do that, another thread can switch
-- 
2.11.0